For example, in a marine container for freezing, an aluminum alloy has been used for many portions of the container because the running cost can be reduced by lightening the container.
Such a marine container for freezing is indispensable to transport frozen goods and perishables. More than 100 containers are loaded on one freighter, and in a container ship, there is a case where many containers more than 1,000 are loaded, and the economical advantage due to the lightening is great. Although the tare weight of a present aluminum-alloy freezing container used as a marine container having a width of about 2.4 m, a length of about 12 m and a height of about 2.9 m is about 4 tons, further lightening such a container almost has not been performed for these ten or more years since a steel material had been changed to an aluminum-alloy material.
Most of present freezing containers are fabricated by welding a sandwich panel having aluminum-alloy skins to an aluminum-alloy frame together with a reinforcing material such as a steel gusset, thereby constructing a box structure. In the above-described marine container, it is necessary to fabricate many parts, and in such a container, not only the weight is great but also much time and cost are required for the fabrication and production.
Further, in a present freezing container, it is necessary to use upper and lower girders, corner posts and floor beams having great section moduli in order to ensure the strength and rigidity of the whole of the container, and this is one of factors obstructing to lighten the container.
As a method for solving the above-described problems in a freezing container, for example, "HIGH-PERFORMANCE Composites September/October 1995" proposes a marine freezing container wherein flanges for connection are provided around a sandwich panel having skins made from a pultruded FRP hollow material and a core made from a foam material, and sandwich panels adjacent to each other are connected by adhesion via the flange, thereby forming a box structure.
In this container, however, because large-scale upper and lower girders, corner posts and floor beams (hereinafter, also referred to as "girders etc.") are not required, the container is lightened as compared with the conventional aluminum-alloy container, but a thick sandwich panel is required to disuse the girders etc., the advantage for lightening is not sufficient. Further, because a structure for connecting panels adjacent to each other is employed, not only the airtight and heat insulating properties are poor but also much time and cost still are required for the fabrication and production.
Also in air cargo containers, there are similar problems.
An airplane has a great gloss factor among various carriages and the influence due to lightening is great even in a small lightening, and therefore, FRP has been used for many portions of a plane body.
Such an air cargo container is indispensable to transport freight and baggages of passengers. Several tens containers are loaded on one airplane, particularly, an airplane used for an international air line, and in a cargo airplane, more than 100 containers are loaded, and the economical advantage due to the lightening is great. Although the weight of a present standard air cargo container having a width of about 2 m, a depth of about 1.5 m and a height of about 1.6 m is about 90 kg, lightening such a container almost has not been performed for these twenty or more years in spite of a known condition where, if the total weight of an airplane, particularly, an airplane used for an international air line, could be reduced by 1 kg, the running cost can be can be reduced by about 100 dollars per one year.
Most of present air cargo containers are fabricated by connecting an aluminum-alloy plate to an aluminum-alloy frame together with a reinforcing material such as a gusset by rivets or welding, thereby constructing a box structure. In the above-described standard container, more than 50 parts must be assembled, and the number of rivets required for the connection is over 500. In such a container, not only the weight is great but also much time and cost are required for the fabrication and production.
Further, in a present air cargo container, it is necessary to use frames having a great section modulus in order to ensure the strength and rigidity of the whole of the container, and this is one of factors obstructing to lighten the container.
As a method for solving the above-described problems in an air cargo container, for example, JP-A-HEI 6-48480 (EP-A-520745) proposes an air cargo container wherein flanges for connection are provided around a sandwich panel having skins made from FRP and a core made from a foam material, and sandwich panels adjacent to each other are connected via the flange, thereby forming a box structure.
In this container, however, because FRP is used and large-scale frames are not required, the container is lightened as compared with the conventional aluminum-alloy container, but a thick sandwich panel is required to achieve a frameless condition, the advantage for lightening is not sufficient. Further, because a structure for connecting panels is employed, much time and cost still are required for the fabrication and production.